Table of Contents

Overview

Hawaii’s Sea Level Is Rising

And Initial Solutions Will Cost Over $1 Billion

The sea level off Hawaii’s coast is up to 10 inches higher than it was in 1950.1 This increase is mostly due to ice melting into the ocean2 and sinking land,3 and it’s causing major issues. Solutions in Hawaii can be complicated because each island is affected differently by sea level rise and flooding, but the impact is felt by all islands collectively.4 The state is planning over $6 billion in sea level rise solutions, which include port and canal improvements, dredging, and restoration of wetland habitats.

Sea level rise is speeding up

The sea level around Hilo Bay, Hawaii, has risen by 10 inches since 1950. Its speed of rise has accelerated over the last ten years and it’s now rising by about 1 inch every 4 years.1 Scientists know this because the sea level is measured every 6 minutes using equipment like satellites, floating buoys off the coast, and tidal gauges to accurately measure the local sea level as it accelerates and changes.6

Created with Highcharts 6.2.0

Sea level measurement from Hilo Bay area tide gauge since 1950

Causes & Complications

Why Are Sea Levels Rising?

While there are four main causes of sea level rise in Hawaii, ice melt2 and land sinkage3 are the largest contributors. Because the rate of ice melt has been increasing significantly since 1992 and the land is sinking due to a process called subsidence, Hawaii is particularly vulnerable to an increased rate of sea level rise in the future. Click here to learn more about the causes of sea level rise.

How Ice Melt Increases Sea Level Rise

How Land Sinkage Increases Sea Level Rise

Solutions aren’t simple

Even though sea level rise is affecting each of the state’s islands differently, the impact is felt by all of the islands collectively. Due to population size and extensive urbanization, Oahu is experiencing the impacts of sea level rise and flooding more than all of the other islands combined. This has a great effect on the rest of Hawaii’s islands, even though they are not experiencing sea level rise as severely.4

Solutions can be complicated in Hawaii because past efforts to protect beaches, which relied on “hard infrastructure” like seawalls, actually contributed to faster coastal erosion and beach loss.7 To protect coastal communities and beaches, the state will need to find policies that discourage hard infrastructure and encourage development further inland.

Forecast

What's the Future of Sea Level Rise?

In the last decade, the speed at which Hawaii’s sea level is rising has increased, and is rising by as much as 1 inch every 4 years. Around Hilo Bay, it took 17 years for the sea level to rise around 6 inches.1 Scientists now forecast that in just the next 12 years, the sea level will have risen by another 6 inches.8

Scientists are not certain how fast the ocean will warm and ice will melt. They expect water levels to continue to rise faster, but are not sure just how fast. Therefore scientists from the National Oceanic and Atmospheric Administration (NOAA) and the US Army Corps of Engineers (USACE) have made predictions based on ranges from low to high.

Below you can see the range of the NOAA and USACE high and intermediate forecasts for various locations around Hawaii.9 Currently, the USACE high forecast, seen as the darkest red line, is the most likely projection.

Nawiliwili

Created with Highcharts 6.2.0Nawiliwili Sea Level Rise Forecasts

Flooding

Flooding Even When There's No Rain

Drainage systems are designed to channel excess rainwater from the streets and drain it into the sea. But with the pressure from rising sea levels and higher tides, seawater can get pushed into these pipes and spill out into the streets. This causes flooding even on days without rain.

Increased storm surge flooding

Unfortunately, slightly higher sea levels make storms like offshore cyclones or hurricanes even more damaging. Higher sea levels create a higher launching point for storm surge, so just a few more inches of sea level rise allow storms to push more water onto the land, even if it doesn’t make landfall.

Hurricane Iniki, 1992

In 1992, Hurricane Iniki hit Hawaii, bringing with it 143 mph gusts of wind and widespread damage, particularly to the south shore of Kauai.10 Iniki was one of only two hurricanes to make landfall in Hawaii. Without sea level rise, Hurricane Iniki’s 6 foot storm surge would have been much lower.

Hurricane Iniki, 1992

Costs

What's at Risk in Hawaii?

There’s a lot at risk from sea level rise and flooding in Hawaii. Flooding from sea level rise can submerge land, endangering important water, sewage, and electrical infrastructure.4 Sea level rise also threatens the state’s coral reefs, which are an important source of food and carry cultural significance as a crucial part of Kumulipo, the Hawaiian story of creation.12 Land loss from coastal erosion worsened by sea level rise could also pose problems for the state and its economy. Loss of land along Hawaii’s coastlines would not only impact homes, businesses, and development sites, but would leave important farmland and habitats at risk of being lost to ocean waters.4